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Permalink Reply by Alexander Noot on January 23, 2013 at 15:36

First of all.....it's annEAling. But hey, typos happen.

Second of all....which steel type are you talking about? Because this can make a MASSIVE difference.

Third.....Degrees fahrenheit or Celcius?

4th.....what hardness will you be aiming for? What size blade with what function? Chopper? Scalpel? This'll make a large difference in heat treatment as well as steel type.

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Permalink Reply by kenneth stout on March 29, 2013 at 5:54

OK,I worked in a heat treat factory for 13 yrs. Annealing  is the process of changing the molecular structure of the steel,as if it had never been heated and quenched before. Heat the metal cherry red and immediately if not sooner,plunge it completely into a bucket of sand and cover completely with3-6 in. of sand.Remove after 24 hrs. and metal will be soft.You may then heat and quench, following with a temper at 300 deg. for 3 hrs; preferably using circulation of air to ensure even heating.If you have access to a Rockwell hardness tester, 55 RC - 58 RC should be about right. I have tested Buck knives and that is their preffered hardness. If you are working with metal that has been properly heated and quenched,the process is then known as tempering,for which you follow the previous mentioned time and temperature. I hope this helps you.  Ken

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Permalink Reply by Don "Cossack Gearhead" Godard on March 29, 2013 at 20:00

Thanks for the info I am getting close to putting it all together

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Permalink Reply by kenneth stout on March 29, 2013 at 22:04

you are very welcome indeed my friend

Don "Cossack Gearhead" Godard said:

Thanks for the info I am getting close to putting it all together

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KnifeMakerPermalink Reply by Carl Rechsteiner on December 9, 2013 at 7:14

In order to answer your question, you need to be more specific about what steel(s) you are using. Proper thermal cycling is steel composition specific. As each steel has it's original designed purpose, it also has criteria for thermal cycling to help it reach it's optimum goal. Annealing, normalizing, hardening, tempering are all part of thermal cycling. Different temperatures and time elements are required for different steels for optimization.

Kenneth has answered your question in a general sense, however, cherry red is a subjective term and varies with the individual's ability to discern shades of color. Also different steels reach "cherry red" at different temps...so back to what steel? Yes, his procedure will work for some steels, but not for all steels suitable for cutlery. Many require several levels of temperature/soak time to achieve true annealing. With most cutlery steels his method will accomplish a very good normalization which is usually "good enough" for most applications. It really depends on how sophisticated and indepth you want to go with this.

Keep in mind alloyed steels add complications you won't have with simple hi-carb steels in the 10XX category. Start adding alloys and trace elements and things change quite a bit.

Also, it would be helpful to know what kind of equipment you are using to do your heating, what kind of controls and temperature monitoring you have on hand, etc. Be as specific as possible to get the best response. Lot of physics going on with the thermal cycling of steels.

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KnifeMakerPermalink Reply by Kevin Davey on June 5, 2015 at 18:52

A lot of good advice above.

Below is a rough rule of thumb for simple carbon steels (it can get very complicated!)

If its annealing (to soften) its often best  to use a dark workshop so you can judge the colors more accurately. Slowly heat it till its cherry red. Have a magnet handy and when the steel loses its magnetism then its about the right temperature. Dont go much higher.  The slower it cools the better (suggestions above).

If it overheats (yellow) then you need to normalize (best done for forged knife before heat treatment). Same as above but do it a couple of times but no need to slow the cooling effect down as much. From a red non magnetic heat to black should do.

If you heat the steel to non magnetic in a dark room, as the steel cools there will be a thermal reaction and it will actually get brighter before going dull again. Thats the color your aiming for for a normalizing temperature (rule of thumb only).

If its tempering, like has been said, depends on the steel  and hardness you want. My  rule of thumb was to clean the blade after hardening so its bright and put in in an electric oven at about 400F. After an hour or so it should start to change color. Blue is often associated with spring tempering so that may be too soft for a cutting edge. Aim for a yellow/brown. Purple is usualy too much but I found out it was ok for some alloys like 52100.  Tempering is going to be trial and error and a lot of edge testing till you find what works for your type of steel and the performance you are looking for.

As you get to learn your steel you may raise or lower the oven temperatures and soak times.

If its a known steel alloy, then you maybe able to get hold of the heat treating specs from the manufacture and use that as a guide. If you want to be real precise and get the same results each time then a digital heat treating kiln is the only real way to go.

As has been mentioned, the whole thermo cycling and heat treatment theories can be a can of worms. You just have to experiment and find out what works best for you with what equipment you have.

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